1. Field of the Invention
The present invention relates to a power conversion technology, more particularly, to a non-isolated inverter and a related control manner thereof and an application using the same.
2. Description of the Related Art
Inverter is a power conversion apparatus, and is usually configured to convert a DC input power into an AC output power by switching multiple power semiconductor devices such as SCRs, GTOs, GTRs, IGBTs or power MOSFETs.
An isolated photovoltaic (PV) grid-connected inverter with power-frequency or high-frequency transformer is generally applied in a PV grid-connected system, so as to ensure the electrical isolation between the power-grid and the PV grid-connected system, and thus providing the personal protection and avoiding the common-mode currents (i.e., leakage currents) between the PV grid-connected system and the ground. However, the power-frequency transformer has the disadvantage of large volume, heavy weight and high cost. On the other hand, the power conversion circuit would be divided into multiple stages if the high-frequency transformer is applied, such that the power conversion circuit has the complexity of control, so as to reduce the system efficiency.
In order to overcome the problem of the isolated PV grid-connected system with the transformer, a transformer-less non-isolated inverter is developed. A transformer-less non-isolated single-phase PV grid-connected inverter has the advantage of small volume, high efficiency and low cost, wherein the most outstanding advantage is that the system efficiency can be increased to 97% to 98%. Accordingly, the transformer-less non-isolated inverter topology is very suitable for the high cost PV power generation grid-connected system, such that the transformer-less non-isolated inverter topology is widely applied in the small-power PV grid-connected system. However, in the transformer-less non-isolated PV grid-connected system, there are electrical connections between the power-grid and the PV array. Since the parasitic capacitors exist between the PV array and the ground, the common-mode currents (i.e. leakage currents) would be generated, such that the electromagnetic interference (EMI) and the potential safety hazard would be increased.